1. Technical Field
The invention relates to dispensing precise quantities of a hot-melt adhesive in exact locations on an object. In particular, the invention relates to a compact unit including an adhesive feed assembly and a positive displacement dispenser mounted closely together by an inlet block, which unit is mounted on a two or three-dimensional motion system and is connected to a control unit which maintains the temperature of the adhesive at critical levels as it moves through the unit and dispensed onto the object.
2. Background Information
The dispensing of extremely small amounts or shots of flowable materials at a precise location in a rapid and controlled manner presents a challenge to those in the dispensing art due to the viscosity of the materials and the extremely small amounts that must be precisely delivered at a precise location on an object. This is especially critical where the adhesive is a hot-melt moisture cured adhesive which is extremely temperature sensitive, and once heated, remains in a stable state for only a certain duration of time, thereby requiring it to be maintained at a certain temperature and dispensed within that time period to prevent the adhesive curing within the dispensing equipment, requiring expensive and time consuming cleaning of the dispensing equipment and disposal of the remaining adhesive, which increase the manufacturing costs of the objects onto which the adhesive is being dispensed.
Various types of positive displacement dispensers, such as shown in U.S. Pat. Nos. 5,350,084 and 5,458,275, provide for positive displacement of adhesives. However, the adhesives used in these types of machines are not always temperature critical nor are they supplied in cartridges, and thus are not concerned with the problem of maintaining a critical temperature of the adhesive being dispensed from the supply adhesive in a replaceable cartridge through the dispenser.
Other devices, such as distributed by Minnesota Mining and Manufacturing Company under their Trademark JET WELD provide a dispenser which maintains an adhesive contained within a cartridge at a certain temperature to prevent premature curing thereof. However, these dispensing systems do not accurately control and dispense extremely precise amounts of the adhesive as does a positive displacement dispenser, as discussed above.
Furthermore, it is desirable for many repetitive tasks to mount the dispenser and adhesive supply on a motion control system for repetitive uniform motion of the dispenser for accurately and repeatedly dispensing the adhesive on the objects as they move into position adjacent the control system, while maintaining the constant uninterrupted flow of the adhesive, wherein the temperature is maintained at precise levels throughout the system, and which enables the assembly line-type production to be continuously maintained with very little down time.
These problems are difficult to overcome with the available mechanisms currently in use today for dispensing certain types of temperature sensitive adhesives, and in particular a hot-melt adhesive which is moisture cured relatively quickly after being exposed to the atmosphere, and when used with an adhesive having a relatively short life once heated to a desired temperature.
Therefore, the need exists for a system, method, and apparatus for accurately dispensing small amounts of a hot-melt adhesive which cures within a limited time period after being heated and exposed to the atmosphere, in a compact, highly efficient and reliable apparatus and method of dispensing.